Commercial telecommunications satellites generate approximately 75% of the entire geostationary earth orbit (GEO) space sector revenue. Their operational life spans between 12 and 15 years, and these limits are largely imposed by the amount of fuel available for station keeping. All on-board systems might be capable of functioning properly for a long time, but without propellant, the satellite cannot maintain its operational orbit—it drifts from its operational orbit and therefore cannot support the communication mission requirements. A non-operational satellite that remains in space is considered space debris. To mitigate the problem of accumulating space debris, a UN policy requires that “at the end of operational life, geostationary spacecraft should be placed in a disposal orbit that has a perigee at least 300 km above the geostationary orbit”. The Federal Communications Commission (FCC) passed a similar regulation in 2004. To comply with these regulations, when relatively little propellant remains, satellites use their residual station-keeping propellant to deorbit and often sacrifice several months of their design lifetime, which corresponds to a significant loss of economic value.
If on-orbit station keeping and tugging services were available, GEO satellites could be left in operational orbits until their propellant supplies were completely exhausted and then transferred to a disposal orbit by a tug. This alternative would bring additional revenue to the satellite operators due to the extended use of on-board transponders. Moreover, GEO satellites could be left in operational orbits even after their propellant supplies are completely exhausted, by providing station keeping services by the space tug service satellite, as will be explained later.
A tugging service, or life extension mission, might be complicated. Several concepts were discussed in the past. Some of these suggestions involved using large satellites and, eventually, more expensive solutions which were likely to be over the threshold of commercial viability. Others propose refueling services, which may be difficult to accomplish when the served satellite wasn't pre-designed for such service. Another complexity is that the current in-space satellites were not designed for service, and have different shapes and mechanical/electrical/propellant interfaces.
Accordingly, there is a need for a solution that will enable a variety of satellites which are approaching the last period of propellant service to utilize and completely exhaust their propellant means for the satellite's original mission, leaving the mission of tugging the exhausted satellite to disposal orbit to an external service. Such external service should be able to serve a variety of different satellites, designed and launched over many years, and should be commercially viable. Preferably, such external service should also be able to provide station-keeping services and other services such as relocation of satellite in a new orbital slot, reutilizing of already inclined satellites and orbit correction of misplaced satellites, to further maintain the useful life of a satellite lacking propellant but still having functioning mission systems.